In recent years, there has been a demand regarding disk array systems for realization of high performance, high capacity, downsizing and so on. Especially, in order to realize the high performance it is necessary to improve processing speed and interface speed of each device. The improvement of the interface speed means to increase signal frequency on transmission lines. If the signal frequency on transmission lines increases as above, signal loss will increase and the influence of signal reflection noises on parts where impedance mismatch occurs will increase, thereby causing errors at a signal transceiver. Therefore, concerning prior disk array systems, it is necessary to investigate the causes of the errors at the signal transceiver and to take necessary measures.
Regarding the prior disk array systems, the interface speed of a hard disk drive on a disk unit is 4 Gbps, but the interface speed of the next generation model will reach to 6 Gbps, which results in an increase in the signal frequency. If the frequency increases in this way, signal loss on transmission lines will increase as mentioned above and the signal reflection noises caused by impedance mismatch will increase, thereby increasing the influence on degradation of the signal quality. As a result, the probability of error occurrence will increase. Therefore, with the prior disk array systems, the signal quality that satisfies a specified error rate can be secured by setting parameters, such as amplitude and pre-emphasis, to each port of a transmitter for an expander contained in the disk unit (referring to Patent Literature 1).